where in the second line we rewrote the amplitude in the dispersive representation using partial fractions. For scattering of external scalars, a similar model with \(m_{1}=m_2\)  was considered in [1]}. This amplitude saturates the tree-level Regge bound and it has an accumulation point in its spectrum, by which we mean that the residue of the amplitude at either \(m_1\)  or \(m_2\)  involves infinitely many particles of all spins in the partial-wave expansion. Such models should not be considered physical, but nevertheless it is useful to illustrate
features when LSD is violated.
